Uv-led curable compositions and inks

ABSTRACT

A radiation curable composition for UV LED curing includes at least one co-initiator selected from the group consisting of an aliphatic tertiary amine and a dialkyl aniline derivative; and at least one specific carbazole photoinitiator. The radiation curable composition can be advantageously used to prevent unstable yellowing behaviour in an image upon storage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2010/068391, filed Dec. 6, 2010. This application claims thebenefit of U.S. Provisional Application No. 61/267,465, filed Dec. 8,2009, which is incorporated by reference herein in its entirety. Inaddition, this application claims the benefit of European ApplicationNo. 09178162.5, filed Dec. 7, 2009, which is also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to radiation curable compositions suitablefor UV LED curing, comprising at least one specific carbazole basedinitiator and an amine co-initiator.

2. Description of the Related Art

Photoinitiators are frequently used in polymerizable compositions, suchas UV-curable inks, to initiate the polymerization of monomers whenexposed to UV radiation. Bathochromic photoinitiators, absorbing in theregion between 365 nm and 395 nm, are required to make full use of therecent development of UV-LEDs with increasing power. Thioxanthones andacyl phosphine oxides are photoinitiators absorbing in this spectralregion.

Thioxanthones are prone to yellowing upon exposure, thereby formingdegradation products with a limited stability. As a result, the originalyellowing shifts upon storage. Especially in imaging, e.g. inkjetprinting, this unstable yellowing behaviour makes control of the imagetone in the final image difficult. On top of that, certain applications,predominantly packaging applications, prefer thioxanthone free radiationcurable compositions.

Acyl phosphine oxides, on the other hand, result in medium volatilealdehyde type of degradation products, resulting in a background smellof the printed image, which is unacceptable in packaging applications.

Therefore, there is an increasing demand for the development of newphotoinitiators, absorbing in the region between 365 nm and 395 nm,having a stable yellowing behaviour without generating medium volatiledegradation products. Recent evolutions in bathochromic photoinitiatorsare based on carbazole derivatives.

Much effort in carbazole based initiators has been directed towards thedevelopment N-acyl oxime derivatives of bis ketocarbazoles asphotoinitiators for black resists as recently reviewed by Dietliker etal. (Progress in Organic Coatings 58, 146-157 (2007) and disclosed in WO2008/138733 (CIBA), WO 2008/138732 (CIBA), WO 2008/138724 (CIBA), WO2007/071497 (CIBA), WO 2007/062963 (CIBA), WO 2006/018405 (CIBA), WO2004/050653 (CIBA), WO 02/100903 (CIBA), WO 2008/075564 (MITSUBISHICHEMICAL) and WO 2006/059458 (ASAHI DENKA).

Carbazole based Norrish type I initiators have been disclosed in JP2007-254701 (TOYO INK), US 2003199601 (SAMSUNG ELECTRONICS), JP63-168403 (FUJI PHOTO FILM) and EP 284561 A (CIBA)).

Bis-keto-carbazoles have been disclosed in photochemical applications assensitizers for acyl oxime and oxime based photoinitiators in negativeresist application (JP 2007-219362 (TOYO INK)) and radiation curableapplications JP 2007-112930 (TOYO INK) and JP 2005-187678 (TOYO INK)).They have further been disclosed as sensitizing agents for cationicradiation curable formulations in US 2005113483 (KONICA MINOLTA), JP2005-343847 (TOYO INK), JP 2000-239648 (JSR) and Yamamura et al.,Journal of Photopolymer Science and Technology, 13(1), 117-118 (2000))and JP 2001-109142 (JSR)).

JP 2005-113043 (KONICA) discloses a cationically UV curable inkjet inkcomposition containing an aliphatic tertiary amine andN-ethyl-3,6-bis(benzoyl)-carbazole photoinitiator. JP 2005-113043(KONICA) is silent on free radical UV curable inkjet ink compositions.

JP 2006-162784 (TOPPAN PRINTING) discloses a photosensitive coloredcomposition including a photopolymerization initiator, aphotopolymerizable monomer, a resin, a pigment and a solvent, wherein aoxime ester compound is used as the photopolymerization initiator. AlsoEP 1395615 (CIBA) AND EP 1567518 (CIBA) disclose UV curable compositionsincluding oxime ester compounds as the photopolymerization initiator.

The carbazole initiators, disclosed in the prior art often requiremultistep synthesis and are often still to hypsochromic to be cured byLED curing. Therefore, there is still a need for easy accessiblephotoinitiators exhibiting high curing speed upon LED exposure.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, it has beensurprisingly found that radiation curable compositions containing atleast one specific carbazole based photoinitiator and at least one aminebased co-initiator could be cured at high curing speed upon exposure toUV radiation in the range between 365 nm and 395 nm.

According to preferred embodiments of the present invention, radiationcurable compositions having a much more stable yellowing behaviour andwithout generating medium volatile degradation products can be achieved,as defined below.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present inventionhereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “C.I.” is used in disclosing the present application as anabbreviation for Colour Index.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

The term “substituted” in, for example substituted alkyl, means that thesubstituent contains at least one atom different from carbon orhydrogen. The substituent may be a single atom, e.g. a halogen, or agroup of atoms containing at least one atom different from carbon orhydrogen, e.g. an acrylate group.

Radiation Curable Compositions

The radiation curable composition according to a preferred embodiment ofpresent invention includes at least one co-initiator selected from thegroup consisting of an aliphatic tertiary amine and a dialkyl anilinederivative; and at least one photoinitiator according to Formula (I):

wherein,R1 and R2 are independently selected from the group consisting of asubstituted or unsubstituted aromatic or heteroaromatic group and asubstituent according to Formula (II):

R3 is selected from the group consisting of hydrogen, a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkenyl group,a substituted or unsubstituted alkynyl group, a substituted orunsubstituted aralkyl group, a substituted or unsubstituted alkarylgroup and a substituted or unsubstituted aryl or heteroaryl group;S1 and S2 are independently selected from the group consisting ofhydrogen, a substituted or unsubstituted alkyl group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted alkynylgroup, a substituted or unsubstituted aralkyl group, a substituted orunsubstituted alkaryl group, a substituted or unsubstituted aryl, asubstituted or unsubstituted heteroaryl group, a halogen, OH, an alkoxygroup, a thiol group, a thioalkoxy group, an ester group, an amidegroup, an amine group and a carboxylic acid group;Y represents O or NR5;R4 and R5 are selected from the group consisting of hydrogen, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted alkynyl group, asubstituted or unsubstituted aralkyl group, a substituted orunsubstituted alkaryl group and a substituted or unsubstituted aryl orheteroaryl group;n and m independently represent an integer from 1 to 3; andX and Z represent O.

In a preferred embodiment at least one of R1 and R2 is represented by asubstituent according to general formula II. In a further preferredembodiment S₁ and S₂ represent hydrogen. In an even further preferredembodiment R3 represents a substituted or unsubstituted alkyl group, abranched alkyl group being particularly preferred.

In a preferred embodiment, the photoinitiator, according to the presentinvention is a diffusion hindered photoinitiator selected from the groupconsisting of a polymerizable photoinitiator, a multifunctionalphotoinitiator and a polymeric or an oligomeric photoinitiator.

In a particularly preferred embodiment the photoinitiator according togeneral structure I comprises at least one polymerizable ethylenicallyunsaturated group, preferably selected from the group consisting of anacrylate, a methacrylate, an acrylamide a methacrylamide, a styrene, amaleimide, a vinyl ester, a vinyl ether, an allyl ether and an allylester, an acrylate and a methacrylate being more preferred and anacrylate being particularly preferred. In an even further preferredembodiment, at least one of R1 to R3 is substituted with at least onepolymerizable ethylenically unsaturated group, preferably an acrylate ora methacrylate, an acrylate being particularly preferred.

In a further preferred embodiment one of the groups selected from R1 toR3 and S₁ and S₂ is linked to a polymer, a star polymer, a dendriticpolymer and a hyperbranched polymer being particularly preferred,polyethers and polyesters being most preferred.

Suitable examples of photoinitiators according to Formula (I) are givenby Table 1, without being limited thereto.

TABLE 1

INI-1

INI-2

INI-3

INI-4

INI-5

INI-6

INI-7

INI-8

INI-9

 INI-10

 INI-11

However for safety reasons, in particular for food packagingapplications, the photoinitiator is preferably a so-called diffusionhindered photoinitiator. A diffusion hindered photoinitiator is aphotoinitiator which exhibits a much lower mobility in a cured layer ofthe curable liquid or ink than a monofunctional photoinitiator, such asbenzophenone. Several methods can be used to lower the mobility of thephotoinitiator. One way is to increase the molecular weight of thephotoinitiator so that the diffusion speed is reduced, e.g. polymericphotoinitiators. Another way is to increase its reactivity so that it isbuilt into the polymerizing network, e.g. multifunctionalphotoinitiators and polymerizable photoinitiators. The diffusionhindered photoinitiator is preferably selected from the group consistingof non-polymeric multifunctional photoinitiators, polymericphotoinitiators and polymerizable photoinitiators. Non-polymericmultifunctional photoinitiators are considered to have a molecularweight between 300 and 900 Dalton. Non-polymerizable monofunctionalphotoinitiators with a molecular weight in that range are not diffusionhindered photoinitiators. Most preferably the diffusion hinderedphotoinitiator is a polymerizable initiator.

Suitable polymerizable photoinitiators according to Formula (I) aregiven by Table 2 without being limited thereto.

TABLE 2

INI-12

INI-13

INI-14

INI-15

INI-16

INI-17

Suitable multifunctional photoinitiators according to Formula (I) aregiven by Table 3, without being limited thereto.

TABLE 3

INI-18

INI-19

Suitable polymeric photoinitiators according to Formula (I) are given byTable 4, without being limited thereto. A specific degree ofsubstitution is given for the sake of clarity.

TABLE 4

INI-20

INI-21

A preferred amount of photoinitiator is 0.1-50 wt %, more preferably0.1-20 wt %, and most preferably 0.3-15 wt % of the total weight of thecurable pigment dispersion or ink.

In order to increase the photosensitivity further, the radiation curablecomposition contains a co-initiator. Suitable examples of co-initiatorscan be categorized in 3 groups:

(1) tertiary aliphatic amines such as methyldiethanolamine,dimethylethanolamine, triethanolamine, triethylamine andN-methylmorpholine;(2) aromatic amines such as amylparadimethylaminobenzoate,2-n-butoxyethyl-4-(dimethylamino) benzoate,2-(dimethylamino)ethylbenzoate, ethyl-4-(dimethylamino)benzoate, and2-ethylhexyl-4-(dimethylamino)benzoate; and(3) (meth)acrylated amines such as dialkylamino alkyl(meth)acrylates(e.g., diethylaminoethylacrylate) or N-morpholinoalkyl-(meth)acrylates(e.g., N-morpholinoethyl-acrylate).The preferred co-initiators are aminobenzoates.

The one or more co-initiators included into the radiation curablecomposition according to a preferred embodiment of the present inventionare preferably diffusion hindered for safety reasons, in particular forfood packaging applications.

A diffusion hindered co-initiator is preferably selected from the groupconsisting of non-polymeric multifunctional co-initiators, oligomeric orpolymeric co-initiators and polymerizable co-initiators. More preferablythe diffusion hindered co-initiator is selected from the groupconsisting of polymeric co-initiators and polymerizable co-initiators.Most preferably the diffusion hindered co-initiator is a polymerizableco-initiator having at least one (meth)acrylate group, more preferablyhaving at least one acrylate group.

Preferred diffusion hindered co-initiators are the polymerizableco-initiators disclosed in EP 2053101 A (AGFA GRAPHICS) in paragraphs[0088] and [0097].

Preferred diffusion hindered co-initiators include a polymericco-initiator having a dendritic polymeric architecture, more preferablya hyperbranched polymeric architecture. Preferred hyperbranchedpolymeric co-initiators are those disclosed in US 2006014848 (AGFA)incorporated herein as a specific reference.

The curable pigment dispersion or ink preferably comprises the diffusionhindered co-initiator in an amount of 0.1 to 50 wt %, more preferably inan amount of 0.5 to 25 wt %, most preferably in an amount of 1 to 10 wt% of the total weight of the ink.

The radiation curable composition according to a preferred embodiment ofthe present invention can be used to prevent unstable yellowingbehaviour in an image upon storage, e.g. an inkjet image.

In a preferred embodiment, the radiation curable composition is aradiation curable inkjet ink, especially an inkjet ink curable by UVLEDs emitting in the spectral region of 365 nm to 395 nm. Due to theircompactness, UV LEDs can be built into inkjet printers more easily thanother UV light sources such as doped mercury lamps.

In a preferred embodiment, the radiation curable inkjet ink is part ofan inkjet ink set, preferably an inkjet ink set including two or moreinkjet inks in accordance with the invention. The radiation curableinkjet ink form preferably part of a CMY(K) inkjet ink set. The CMY(K)inkjet ink set may also be extended with extra inks such as red, green,blue, violet and/or orange to further enlarge the colour gamut of theimage. The CMY(K) ink set may also be extended by the combination offull density and light density inks of both colour inks and/or blackinks to improve the image quality by lowered graininess.

The inkjet ink can be advantageously used in an inkjet printing methodcomprising the steps:

a) providing a radiation curable inkjet ink according to a preferredembodiment of the present invention; andb) jetting the inkjet ink onto an ink-receiver.

The radiation curable composition according to a preferred embodiment ofthe present invention may further also contain at least one surfactantto control the homogenous spreading of the pigment dispersion on asubstrate. For an inkjet ink, the surfactant is important to control thedot size of the ink droplet on a substrate.

There is no limitation on the viscosity of the radiation curablecomposition, but the viscosity of a radiation curable inkjet ink ispreferably lower than 30 mPa·s, more preferably lower than 15 mPa·s, andmost preferably between 2 and 10 mPa·s at a shear rate of 100 s⁻¹ and ajetting temperature between 10 and 70° C.

The radiation curable composition according to a preferred embodiment ofthe present invention is preferably prepared according to a methodcomprising the steps of:

a) providing a composition containing monomers;b) adding to said composition at least one co-initiator selected fromthe group consisting of an aliphatic tertiary amine and a dialkylaniline derivative; and at least one photoinitiator according to Formula(I).

Monomers and Oligomers

The monomers and oligomers used in radiation curable compositions andinks, especially for food packaging applications, are preferablypurified compounds having no or almost no impurities, more particularlyno toxic or carcinogenic impurities. The impurities are usuallyderivative compounds obtained during synthesis of the polymerizablecompound. Sometimes, however, some compounds may be added deliberatelyto pure polymerizable compounds in harmless amounts, for example,polymerization inhibitors or stabilizers.

Any monomer or oligomer capable of free radical polymerization may beused as polymerizable compound. A combination of monomers, oligomersand/or prepolymers may also be used. The monomers, oligomers and/orprepolymers may possess different degrees of functionality, and amixture including combinations of mono-, di-, tri-and higherfunctionality monomers, oligomers and/or prepolymers may be used. Theviscosity of the radiation curable compositions and inks can be adjustedby varying the ratio between the monomers and oligomers.

Particularly preferred monomers and oligomers are those listed in [0106]to [0115] in EP 1911814 A (AGFA GRAPHICS) incorporated herein as aspecific reference.

A preferred class of monomers and oligomers are vinyl ether acrylatessuch as those described in U.S. Pat. No. 6,310,115 (AGFA), incorporatedherein by reference. Particularly preferred compounds are2-(2-vinyloxyethoxy)ethyl (meth)acrylate, most preferably the compoundis 2-(2-vinyloxyethoxy)ethyl acrylate.

Colorants

Colorants used in the radiation curable compositions and inks may bedyes, pigments or a combination thereof. Organic and/or inorganicpigments may be used. The colorant is preferably a pigment or apolymeric dye, most preferably a pigment.

The pigments may be black, white, cyan, magenta, yellow, red, orange,violet, blue, green, brown, mixtures thereof, and the like. This colourpigment may be chosen from those disclosed by HERBST, Willy, et al.Industrial Organic Pigments, Production, Properties, Applications. 3rdedition. Wiley—VCH, 2004. ISBN 3527305769.

Suitable pigments are disclosed in paragraphs [0128] to [0138] of WO2008/074548 (AGFA GRAPHICS).

Suitable pigments include mixed crystals of the above particularpreferred pigments. Mixed crystals are also referred to as solidsolutions. For example, under certain conditions different quinacridonesmix with each other to form solid solutions, which are quite differentfrom both physical mixtures of the compounds and from the compoundsthemselves. In a solid solution, the molecules of the components enterinto the same crystal lattice, usually, but not always, that of one ofthe components. The x-ray diffraction pattern of the resultingcrystalline solid is characteristic of that solid and can be clearlydifferentiated from the pattern of a physical mixture of the samecomponents in the same proportion. In such physical mixtures, the x-raypattern of each of the components can be distinguished, and thedisappearance of many of these lines is one of the criteria of theformation of solid solutions. A commercially available example isCinquasia Magenta RT-355-D from Ciba Specialty Chemicals.

Also mixtures of pigments may be used in the UV curable inks. For someinkjet applications, a neutral black inkjet ink is preferred and can beobtained, for example, by mixing a black pigment and a cyan pigment intothe ink. The inkjet application may also require one or more spotcolours, for example for packaging inkjet printing or textile inkjetprinting. Silver and gold are often desired colours for inkjet posterprinting and point-of-sales displays.

Non-organic pigments may be used in the radiation curable compositionsand inks. Particular preferred pigments are C.I. Pigment Metal 1, 2 and3. Illustrative examples of the inorganic pigments include red ironoxide (III), cadmium red, ultramarine blue, prussian blue, chromiumoxide green, cobalt green, amber, titanium black and synthetic ironblack.

Pigment particles in inkjet inks should be sufficiently small to permitfree flow of the ink through the inkjet-printing device, especially atthe ejecting nozzles. It is also desirable to use small particles formaximum colour strength and to slow down sedimentation.

The numeric average pigment particle size is preferably between 0.050and 1 μm, more preferably between 0.070 and 0.300 μm and particularlypreferably between 0.080 and 0.200 μm. Most preferably, the numericaverage pigment particle size is no larger than 0.150 μm. An averageparticle size smaller than 0.050 μm is less desirable for decreasedlight-fastness, but mainly also because very small pigment particles orindividual pigment molecules thereof may still be extracted in foodpackaging applications. The average particle size of pigment particlesis determined with a Nicomp 30 Submicron Particle Analyzer based uponthe principle of dynamic light scattering. The ink is diluted with ethylacetate to a pigment concentration of 0.002 wt %.

However for a white UV curable ink, the numeric average particlediameter of the white pigment is preferably from 50 to 500 nm, morepreferably from 150 to 400 nm, and most preferably from 200 to 350 nm.Sufficient hiding power cannot be obtained when the average diameter isless than 50 nm, and the storage ability and the jet-out suitability ofthe ink tend to be degraded when the average diameter exceeds 500 nm.The determination of the numeric average particle diameter is bestperformed by photon correlation spectroscopy at a wavelength of 633 nmwith a 4 mW HeNe laser on a diluted sample of the pigmented inkjet ink.A suitable particle size analyzer used was a MALVERN™ nano-S availablefrom Goffin-Meyvis. A sample can, for example, be prepared by additionof one drop of ink to a cuvet containing 1.5 mL ethyl acetate and mixeduntil a homogenous sample was obtained. The measured particle size isthe average value of 3 consecutive measurements consisting of 6 runs of20 seconds.

Suitable white pigments are given by Table 2 in [0116] of WO 2008/074548(AGFA GRAPHICS). The white pigment is preferably a pigment with arefractive index greater than 1.60. The white pigments may be employedsingly or in combination. Preferably titanium dioxide is used as pigmentwith a refractive index greater than 1.60. Suitable titanium dioxidepigments are those disclosed in [0117] and in [0118] of WO 2008/074548(AGFA GRAPHICS).

The pigments are present in the range of 0.01 to 10% by weight,preferably in the range of 0.1 to 5% by weight, each based on the totalweight of UV curable ink. For white UV curable inks, the white pigmentis preferably present in an amount of 3% to 30% by weight of the inkcomposition, and more preferably 5% to 25%. An amount of less than 3% byweight cannot achieve sufficient covering power and usually exhibitsvery poor storage stability and ejection property.

Generally pigments are stabilized in the dispersion medium by dispersingagents, such as polymeric dispersants. However, the surface of thepigments can be modified to obtain so-called “self-dispersible” or“self-dispersing” pigments, i.e. pigments that are dispersible in thedispersion medium without dispersants.

Dispersants

The dispersant is preferably a polymeric dispersant. Typical polymericdispersants are copolymers of two monomers but may contain three, four,five or even more monomers. The properties of polymeric dispersantsdepend on both the nature of the monomers and their distribution in thepolymer. Suitable copolymeric dispersants have the following polymercompositions:

statistically polymerized monomers (e.g. monomers A and B polymerizedinto ABBAABAB);

alternating polymerized monomers (e.g. monomers A and B polymerized intoABABABAB);

gradient (tapered) polymerized monomers (e.g. monomers A and Bpolymerized into AAABAABBABBB);

block copolymers (e.g. monomers A and B polymerized into AAAAABBBBBB)wherein the block length of each of the blocks (2, 3, 4, 5 or even more)is important for the dispersion capability of the polymeric dispersant;

graft copolymers (graft copolymers consist of a polymeric backbone withpolymeric side chains attached to the backbone); and

mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable polymeric dispersants are listed in the section on“Dispersants”, more specifically [0064] to [0070] and to [0077], in EP1911814 A (AGFA GRAPHICS) incorporated herein as a specific reference.

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30000, more preferably between 1500 and 10000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100000, more preferably smaller than 50000 andmost preferably smaller than 30000.

The polymeric dispersant has preferably a polydispersity PD smaller than2, more preferably smaller than 1.75 and most preferably smaller than1.5.

Commercial examples of polymeric dispersants are the following:

DISPERBYK™ dispersants available from BYK CHEMIE GMBH;

SOLSPERSE™ dispersants available from NOVEON;

TEGO™ DISPERS™ dispersants from EVONIK;

EDAPLAN™ dispersants from MÜNZING CHEMIE;

ETHACRYL™ dispersants from LYONDELL;

GANEX™ dispersants from ISP;

DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;

DISPONER™ dispersants from DEUCHEM; and

JONCRYL™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include SOLSPERSE™dispersants from NOVEON, EFKA™ dispersants from CIBA SPECIALTY CHEMICALSINC and DISPERBYK™ dispersants from BYK CHEMIE GMBH. Particularlypreferred dispersants are SOLSPERSE™ 32000, 35000 and 39000 dispersantsfrom NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt%, more preferably 5 to 200 wt % based on the weight of the pigment.

Dispersion Synergists

A dispersion synergist usually consists of an anionic part and acationic part. The anionic part of the dispersion synergist exhibiting acertain molecular similarity with the colour pigment and the cationicpart of the dispersion synergist consists of one or more protons and/orcations to compensate the charge of the anionic part of the dispersionsynergist.

The synergist is preferably added in a smaller amount than the polymericdispersant(s). The ratio of polymeric dispersant/dispersion synergistdepends upon the pigment and should be determined experimentally.Typically the ratio wt % polymeric dispersant/wt % dispersion synergistis selected between 2:1 to 100:1, preferably between 2:1 and 20:1.

Suitable dispersion synergists that are commercially available includeSOLSPERSE™ 5000 and SOLSPERSE™ 22000 from NOVEON.

Particular preferred pigments for the magenta ink used are adiketopyrrolo-pyrrole pigment or a quinacridone pigment. Suitabledispersion synergists include those disclosed in EP 1790698 A (AGFAGRAPHICS), EP 1790696 A (AGFA GRAPHICS), WO 2007/060255 (AGFA GRAPHICS)and EP 1790695 A (AGFA GRAPHICS).

In dispersing C.I. Pigment Blue 15:3, the use of a sulfonatedCu-phthalocyanine dispersion synergist, e.g. SOLSPERSE™ 5000 from NOVEONis preferred. Suitable dispersion synergists for yellow inkjet inksinclude those disclosed in EP 1790697 A (AGFA GRAPHICS).

Surfactants

The radiation curable compositions and inks may contain a surfactant.The surfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionicand are usually added in a total quantity less than 10 wt % based on thetotal weight of the radiation curable composition or ink andparticularly in a total less than 5 wt % based on the total weight ofthe radiation curable composition or ink.

Suitable surfactants include those disclosed in paragraphs [0283] to[0291] of WO 2008/074548 (AGFA GRAPHICS) incorporated herein as aspecific reference.

Inhibitors

The UV curable compositions and inks may contain a polymerizationinhibitor. Suitable polymerization inhibitors include phenol typeantioxidants, hindered amine light stabilizers, phosphor typeantioxidants, hydroquinone monomethyl ether commonly used in(meth)acrylate monomers, and hydroquinone, t-butylcatechol, pyrogallol,2,6-di-tert.butyl-4-methylphenol may also be used.

Suitable commercial inhibitors are, for example, SUMILIZER™ GA-80,SUMILIZER™ GM and SUMILIZER™ GS produced by Sumitomo Chemical Co. Ltd.;GENORAD™ 16, GENORAD™ 18 and GENORAD™ 20 from Rahn AG; IRGASTAB™ UV10and IRGASTAB™ UV22, TINUVIN™ 460 and CGS20 from Ciba SpecialtyChemicals; FLOORSTAB™ UV range (UV-1, UV-2, UV-5 and UV-8) fromKromachem Ltd, ADDITOL™ S range (S100, 5110, 5120 and 5130) from CytecSurface Specialties.

The inhibitor is preferably a polymerizable inhibitor.

Since excessive addition of these polymerization inhibitors may lowerthe curing speed, it is preferred that the amount capable of preventingpolymerization is determined prior to blending. The amount of apolymerization inhibitor is preferably lower than 5 wt %, morepreferably lower than 3 wt % of the total radiation curable compositionor ink.

Preparation of Curable Inks

The average particle size and distribution of a colour pigment is animportant feature for inkjet inks. The inkjet ink may be prepared byprecipitating or milling the pigment in the dispersion medium in thepresence of the dispersant.

Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a ball mill, a pearl mill, acolloid mill, a high-speed disperser, double rollers, a bead mill, apaint conditioner, and triple rollers. The dispersions may also beprepared using ultrasonic energy.

Many different types of materials may be used as milling media, such asglasses, ceramics, metals, and plastics. In a preferred embodiment, thegrinding media can comprise particles, preferably substantiallyspherical in shape, e.g. beads consisting essentially of a polymericresin or yttrium stabilized zirconium oxide beads.

In the process of mixing, milling and dispersion, each process isperformed with cooling to prevent build up of heat, and as much aspossible under light conditions in which actinic radiation has beensubstantially excluded.

The inkjet ink may contain more than one pigment, and may be preparedusing separate dispersions for each pigment, or alternatively severalpigments may be mixed and co-milled in preparing the dispersion.

The dispersion process can be carried out in a continuous, batch orsemi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grindwill vary widely depending upon the specific materials and the intendedapplications. The contents of the milling mixture comprise the millgrind and the milling media. The mill grind comprises pigment, polymericdispersant and a liquid carrier. For inkjet inks, the pigment is usuallypresent in the mill grind at 1 to 50 wt %, excluding the milling media.The weight ratio of pigment over polymeric dispersant is 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment,mechanical means and residence conditions selected, the initial anddesired final particle size, etc. In a preferred embodiment of thepresent invention pigment dispersions with an average particle size ofless than 100 nm may be prepared.

After milling is completed, the milling media is separated from themilled particulate product (in either a dry or liquid dispersion form)using conventional separation techniques, such as by filtration, sievingthrough a mesh screen, and the like. Often the sieve is built into themill, e.g. for a bead mill. The milled pigment concentrate is preferablyseparated from the milling media by filtration.

In general it is desirable to make the inkjet inks in the form of aconcentrated mill grind, which is subsequently diluted to theappropriate concentration for use in the inkjet printing system. Thistechnique permits preparation of a greater quantity of pigmented inkfrom the equipment. By dilution, the inkjet ink is adjusted to thedesired viscosity, surface tension, colour, hue, saturation density, andprint area coverage for the particular application.

EXAMPLES Materials

All materials used in the following examples were readily available fromstandard sources such as ALDRICH CHEMICAL Co. (Belgium) and ACROS(Belgium) unless otherwise specified. The water used was deionizedwater.

DPGDA is dipropyleneglycoldiacrylate from SARTOMER. TMPTA istrimethylolpropane triacrylate available as SARTOMER™ SR351 fromSARTOMER.

VEEA is 2-(vinylethoxy)ethyl acrylate, a difunctional monomer availablefrom NIPPON SHOKUBAI, Japan.

EPD is ethyl 4-dimethylaminobenzoate, available under the trade name ofGENOCURE™ EPD from RAHN AG.

IC127 is an abbreviation used for IRGACURE™ 127, supplied by CibaSpecialty Chemicals:

IC907 is an abbreviation used for IRGACURE™ 907 is2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, aphotoinitiator available from CIBA SPECIALTY CHEMICALS. IC379 is anabbreviation used for IRGACURE™ 379 is a photoinitiator available fromCIBA SPECIALTY having as chemical structure:

ITX is an abbreviation used for DAROCUR™ ITX, an isomeric mixture of 2-and 4-isopropylthioxanthone from CIBA SPECIALTY CHEMICALS.TPO is an abbreviation used for2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide available under the tradename DAROCUR™ TPO from CIBA SPECIALTY CHEMICALS.GENORAD™ 16 is a polymerization inhibitor from RAHN AG.GENOSOL is a 50 wt % solution of GENORAD™ 16 in DPGDA.

PB15:4 is an abbreviation used for HOSTAPERM™ Blue P-BFS, a cyan pigment(C.I. Pigment Blue 15:4) available from CLARIANT.

DB162 is an abbreviation used for the polymeric dispersant DISPERBYK™162 available from BYK CHEMIE GMBH whereof the solvent mixture of2-methoxy-1-methylethylacetate, xylene and n-butylacetate was removed.DB162sol is a 30 wt % solution of DB162 in DPGDA.S35000 is an abbreviation used for SOLSPERSE™ 35000, apolyethyleneimine-polyester hyperdispersant from NOVEON.S35000SOL is a 40 wt % solution of 535000 in DPGDA.BYK™ UV3510 is a polyether modified polydimethylsiloxane wetting agentavailable from BYK CHEMIE GMBH.

Measurement Methods 1. Curing Speed

The curing speed on a Fusion DRSE-120 conveyer was defined as thepercentage of the maximum output of the lamp needed to cure the samples.The lower the number the higher curing speed. A sample was considered asfully cured at the moment scratching with a Q-tip caused no visualdamage.

A percentage of more then 100% of the maximum output of the lamp meansthat the speed of the conveyer belt had to be reduced to get the samplefully cured at the maximum output of the lamp. The higher thepercentage, the more the belt had to be slowed down. A curing speed of160% means a belt speed of 12.5 m/min at the maximum output of the lamp.A percentage between 150% and 200% is considered as at the edge ofpractical use. A percentage above 200% is considered out of the rangefor practical use and no higher percentages are measured.

2. Curing Degree

The curing degree was tested on a coating immediately after curing withUV light. The cured coating is rubbed with the means of a Q-tip. Whenthe surface is not damaged, the coating is fully cured. When some of thecured coating can be damaged, the coating is only partly cured. When thewhole cured coating is damaged, the coating is not cured.

3. Average Particle Size

The particle size of pigment particles in an inkjet ink was determinedby photon correlation spectroscopy at a wavelength of 633 nm with a 4 mWHeNe laser on a diluted sample of the pigmented inkjet ink. The particlesize analyzer used was a MALVERN™ nano-S available from Goffin-Meyvis.

The sample was prepared by addition of one drop of ink to a cuvettecontaining 1.5 mL ethyl acetate and mixed until a homogenous sample wasobtained. The measured particle size is the average value of 3consecutive measurements consisting of 6 runs of 20 seconds. For goodink jet characteristics (jetting characteristics and print quality) theaverage particle size of the dispersed particles is below 200 nm,preferably between 70 and 150 nm.

4. Image Tone

Printed or coated samples were measured with a spectrophotometer (GRETAGSPM, manufactured by GRETAG INC.) to determine the coordinates of theL*a*b* colours system of the colour difference indication methodspecified in CIE (Commission International de l'Eclairage). In thiscase, the measurement was carried out under conditions of light sourceD50, provision of no light source filter, absolute white as referencewhite, and angle of visibility 2°.

5. Degree of Conversion

The degree of conversion, i.e. the percentage of converted functionalgroups, may be determined by for example RT-FTIR (Real-Time FourierTransform Infra-Red Spectroscopy).

From a radiation curable composition, an FTIR-spectrum, using amicro-ATR method on a BIO-RAD FTS-7 spectrometer, equipped with a splitpea module from Harrick, was taken before curing, by applying a drop ofink on the split pea module. A second sample of the radiation curablecomposition was coated on a PGA-paper, using a bar coater and a 10 μmwired bar. The coated sample was mounted on a belt, transporting thesamples under a Phoseon 4 W 395 nm LED at a speed specified in theexamples.

After coating and curing the radiation curable composition as describedabove, a second FTIR-spectrum was taken from each coated and curedsample under the same conditions. The change in peak height at 810 cm⁻¹,corresponding to a C—H vibration on the double bonds was measuredrelative to the C═O-stretching vibration at 1728 cm⁻¹, which was used asan internal reference and the following two ratios were determined:

ratio_(curing) =I ₈₁₀(curing)/I ₁₇₂₈(curing)

ratio_(ref) =I ₈₁₀(ref)/I ₁₇₂₈(ref)

wherein I corresponds to the respective peak heights. It was assumedthat the ester function remained unchanged during curing. The curingpercentage was calculated as follows:

Curing %=100−(ratio_(curing)/ratio_(ref))*100

A full cure is defined as a degree of conversion wherein the increase inthe percentage of converted functional groups, with increased exposureto radiation (time and/or dose), is negligible. A full cure correspondswith a conversion percentage that is within 10%, preferably 5%, from themaximum conversion percentage defined by the horizontal asymptote in theRT-FTIR graph (percentage conversion versus curing energy or curingtime).

Example 1

This example illustrates the simplicity of the method for preparing aphotoinitiator according to a preferred embodiment of the presentinvention.

Photoinitiator INI-1

First, 9-(2-ethyl-hexyl)-9H-carbazole was synthesized according to thefollowing synthesis scheme:

To a pale brown solution of 9H-carbazole (66.9 g, 0.4 mol),3-bromomethyl-heptane (125.5 g, 0.65 mol) and tetrabutylammoniumhydrogensulfate (37.3 g, 0.11 mol) in acetone (650 ml), potassiumhydroxide (86%) (49.6 g, 0.76 mol) was added in portions. The reactionmixture was heated to reflux temperature and stirred for about 16 hours.The inorganic residues were removed by filtration and the solvent wasevaporated under reduced pressure. The residual oil was dissolved inmethyl-tert-butylether (500 ml) and extracted with distilled water (500ml). The aqueous layer was extracted with dichloromethane (350 ml).

The pooled organic fractions were dried over MgSO₄ and the solvent wasevaporated under reduced pressure to obtain a brown oil. The crude9-(2-ethyl-hexyl)-9H-carbazole was purified on a Merck SVP D40 Columnusing n-hexane as eluent. Evaporation of the pooled fractions yielded 85g of 9-(2-ethyl-hexyl)-9H-carbazole.

Then, 2[6-ethoxyoxalyl-9-(2-ethyl-hexyl)-9H-carbazol-3-yl]-oxo-aceticacid ethyl ester was synthesized according to the following synthesisscheme:

To a solution of 9-(2-ethyl-hexyl)-9H-carbazole (7.0 g, 0.025 mol) indichloromethane (30 ml), ethyloxalyl chloride (7.2 g, 0.0525 mol) wasadded and stirred for 15 minutes at room temperature. The reactionmixture was cooled to −5° C. and aluminium chloride (7.3 g, 0.055 mol)was added in portions while the temperature was maintained below 0° C.The reaction mixture was allowed to stir at room temperature for 1.5hours. The reaction mixture was poured into ice (200 g) and diluted withdichloromethane (100 ml). The organic layer was separated and extracted5 times with distilled water (150 ml). The organic layer was dried overMgSO₄, filtered and the solvent was removed under reduced pressure. Theresidual oil was purified on a Prochrom LC80 Column usingdichloromethane as eluent. Evaporation of the pooled fractions yielded4.3 g of INI-1. (R_(f): 0.25, eluent 100% methylene chloride, MerckKieselgel 60 F₂₅₄).

Photoinitiator INI-2

First, [9-(2-Ethyl-hexyl)-9H-carbazol-3-yl]-phenyl-methanone wassynthesized according to the following synthesis scheme:

To a solution of 9-(2-ethyl-hexyl)-9H-carbazole (7.0 g, 0.025 mol) indichloromethane (30 ml), benzoyl chloride (4.5 g, 0.0525 mol) was addedand stirred for 15 minutes at room temperature. Aluminium chloride (7.3g, 0.055 mol) was added in portions while the temperature was maintainedbelow 30° C. The reaction mixture was allowed to stir at roomtemperature for 15 hours. The reaction mixture was poured into ice (150g) and distilled water (100 ml) and diluted with dichloromethane (200ml). The organic layer was separated and washed with a saturatedsolution of sodium bicarbonate (250 ml) and a saturated solution ofsodium chloride (250 ml). The organic layer was dried over MgSO₄,filtered and the solvent was removed under reduced pressure. Theresidual solid was purified on a Prochrom LC80 Column using ethylacetate/n-hexane (20/80) as eluent. TLC shows a yellow fluorescentproduct with Rf-value of 0.48 in dichloromethane as eluent. Evaporationof the pooled fractions yielded 1.5 g of[9-(2-Ethyl-hexyl)-9H-carbazol-3-yl]-phenyl-methanone.

Then, [6-benzoyl-9-(2-ethyl-hexyl)-9H-carbazol-3-yl]-oxo-acetic acidethyl ester was synthesized according to the following synthesis scheme:

To a solution of [9-(2-ethyl-hexyl)-9H-carbazole-3-yl]-phenyl-methanone(4.4 g, 0.011 mol) in dichloromethane (40 ml), ethyloxalyl chloride (4.3g, 0.03135 mol) was added and stirred for 15 minutes at roomtemperature. Aluminium chloride (4.2 g, 0.03135 mol) was added inportions while the temperature was maintained below 30° C. The reactionmixture was allowed to stir at room temperature for 48 hours. Thereaction mixture was poured into ice (100 g) and distilled water (50 ml)and diluted with dichloromethane (60 ml). The organic layer wasseparated, dried over MgSO₄ and filtered. The solvent was removed underreduced pressure. The residue was purified on a Prochrom LC80 Columnusing dichloromethane as eluent. Evaporation of the pooled fractionsyielded 3.6 g of INI-2 (R_(f): 0.28, eluent: 100% methylene chloride,Merck Kieselgel 60 F₂₅₄).

Photoinitiator INI-3

[6-Benzoyl-9-(2-ethyl-hexyl)-9H-carbazol-3-yl]-phenyl-methanone wassynthesized according to the following synthesis scheme:

To a solution of 9-(2-ethyl-hexyl)-9H-carbazole (7.0 g, 0.025 mol) indichloromethane (30 ml), benzoyl chloride (4.5 g, 0.0525 mol) was addedand stirred for 15 minutes at room temperature. Aluminium chloride (7.3g, 0.055 mol) was added in portions while the temperature was maintainedbelow 30° C. The reaction mixture was allowed to stir at roomtemperature for 15 hours. The reaction mixture was poured into ice (150g) and distilled water (100 ml) and diluted with dichloromethane (200ml). The organic layer was separated and extracted with a saturatedsolution of sodium bicarbonate (250 ml) and a saturated solution ofsodium chloride (250 ml). The organic layer was dried over MgSO₄,filtered and the solvent was removed under reduced pressure. Theresidual solid was purified on a Prochrom LC80 Column using ethylacetate/n-hexane (20/80) as eluent. TLC shows a blue fluorescent productwith Rf-value of 0.15 in dichloromethane as eluent. Evaporation ofpooled fractions yielded 1.5 g of INI-3.

Photoinitiator INI-4

[9-(2-Ethyl-hexyl)-6-(3-methoxy-benzoyl)-9H-carbazol-3-yl]-(3-methoxy-phenyl)-methanonewas synthesized according to the following synthesis scheme:

To a solution of 9-(2-ethyl-hexyl)-9H-carbazole (7.0 g, 0.025 mol) indichloromethane (30 ml), 3-methoxy-benzoyl chloride (9.0 g, 0.0525 mol)was added and stirred for 15 minutes at room temperature. Aluminiumchloride (7.3 g, 0.055 mol) was added in portions while the temperaturewas maintained below 30° C. The reaction mixture was stirred at roomtemperature for 16 hours. The reaction mixture was poured into ice (150g) and distilled water (100 ml) and diluted with dichloromethane (200ml). The organic layer was separated and washed with a saturatedsolution of sodium bicarbonate (250 ml) and a saturated solution ofsodium chloride (250 ml). The organic layer was dried over MgSO₄ andfiltered. The solvent was removed under reduced pressure. The residualsolid was purified on a Merck SVP D40 Column usingdichloromethane/n-hexane (50/50) as eluent. Evaporation of the solventof the different fractions provided 7.1 g of INI-4 (R_(f): 0.6, eluentmethylene chloride/ethyl acetate 90/10, Merck Kieselgel 60 F₂₅₄).

Photoinitiators INI-8 and INI-12

[9-6-(2-ethyl-hexyloxyoxalyl)-9H-carbazol-3-yl)-oxo-acetic acid2-ethyl-hexyl ester was synthesized according to the following synthesisscheme:

The Friedel-Crafts-Acylation:

60 g (0.307 mol) of 9-ethyl-carbazole (supplied by Aldrich) wasdissolved in 250 ml methylene chloride. 92.3 g (0.676 mol) ethyl-oxalylchloride was added. 90 g (0.676 mol) aluminium chloride was addedportion wise, while maintaining the temperature below 35° C. Uponcomplete addition, the reaction mixture was cooled to −10° C. and thereaction was allowed to continue for 24 hours. The reaction mixturebecame difficult to stir. 350 ml ethyl acetate was added at roomtemperature and the reaction mixture was stirred for 16 hours. Thereaction mixture was poured into 360 g ice and an additional 360 mlethyl acetate was added. The organic fraction was isolated, extractedwith brine and twice with 200 ml of a saturated NaHCO₃ solution. Theintermediate diester precipitated from the organic fraction and wasisolated by filtration. The filtrate was evaporated under reducedpressure and the residue was treated with toluene, yielding a secondcrop of the diester. The fractions were pooled and 52.8 g (43.6%) of thediester was isolated (R_(f): 0.23, eluent 70/30 hexane/ethyl acetate onMerck Kieselgel 60 F₂₅₄). The intermediate was used without furtherpurification.

The Hydrolysis of the Esters:

42.8 g (0.108 mol) of the diester was dissolved in 150 ml ethanol. 13 g(0.322 mol) NaOH was added and the reaction mixture was heated to 60° C.The reaction was allowed to continue for one hour at 60° C. 100 ml waterwas added to the reaction mixture and the mixture was acidified to pH=1,using a 6N hydrochloric acid solution. The dicarboxylic acidprecipitated from the medium, was isolated by filtration and dried. 18.7g (52%) of the dicarboxylic acid was isolated. LCMS analysis indicated apurity of 95%. The dicarboxylic acid was used without furtherpurification.

The CDI-Coupling:

7.5 g (22 mmol) of the dicarboxylic acid was dissolved in 20 ml dimethylacetamide. 6.9 g (41 mmol) CDI was added. The temperature rose to 35° C.and the reaction was allowed to continue for 4 hours at 80° C. 5.8 g (44mmol) 2-ethyl-hexyl alcohol was added and the reaction was allowed tocontinue for one hour at 80° C. After one hour, an additional 5.8 g (44mmol) 2-ethyl-hexyl alcohol was added and the reaction was allowed tocontinue at 80° C. for 16 hours. After cooling down to room temperature,150 ml methyl tert.butyl ether and 100 ml water were added to thereaction mixture. The aqueous layer was extracted three times with 100ml methyl tert.butyl ether. The organic fractions were pooled, driedover MgSO₄ and evaporated under reduced pressure. INI-8 was isolated bypreparative column chromatography on a Prochrom LC80 column, usingKromasil Si 60A 10 μm and a gradient elution from 100% methylenechloride to methylene chloride/ethyl acetate 94/6 at a flow rate of 150ml/min. (R_(f): 0.35, eluent MeOH/NaCl 90/10, Partisil KC18F).

INI-12 was isolated as side product in this reaction. (R_(f): 0.25,eluent MeOH/0.5 M NaCl 90/10, Partisil KC18F).

Photoinitiators INI-5 and INI-10

(9-sec.butyl-6-ethoxyoxalyl-9H-carbazol-3-yl)-oxo-acetic acid ethylester (INI-5) and (9-sec.butyl-9H-carbazol-3-yl)-oxo-acetic acid ethylester (INI-10) were synthesized according to the following synthesisscheme:

Alkylation of Carbazole:

25 g (0.15 mol) of carbazole and 33 g (0.24 mol) 2-bromo-butane weredissolved in 250 ml acetone. 14 g (40 mmol) tetrabutylammonium hydrogensulfate was added, followed by the addition of 18.6 g (0.285 mol)potassium hydroxide (88%). The reaction mixture was refluxed for 10hours. After 10 hours, an additional 4 g (30 mmol) 2-bromo-butane and 2g (31 mmol) potassium hydroxide (88%) were added and the reaction wasallowed to continue at reflux temperature for 16 hours. The precipitatedsalts were removed by filtration and the solvent was evaporated underreduced pressure. The residue was redissolved in 200 ml methyltert.butyl ether and extracted with 100 ml 1M Na₂CO₃ and 100 ml water.The organic fraction was isolated, dried over MgSO₄ and evaporated underreduced pressure. N-sec.butyl-carbazole was isolated by preparativecolumn chromatography on a Prochrom LC80 column, using Kromasil Si60 10μm and n. hexane/methylene chloride 93/7 as eluent. 8.7 g (26%) ofN-sec.butyl carbazole was isolated.

Friedel-Crafts Acylation:

8.24 g (37 mmol) of N-sec.butyl-carbazole was dissolved in 50 mlmethylene chloride. 10.6 g (78 mmol) ethyl-oxalyl chloride was added andthe reaction mixture was cooled to −15° C. 10.9 g (82 mmol) aluminiumchloride was added portion wise, while the temperature was kept at −5°C. The reaction was allowed to continue for 10 minutes at −5° C. Thereaction was further allowed to continue for 45 minutes at roomtemperature. The reaction mixture was poured into 300 ml ice. 100 mlmethylene chloride was added. The organic fraction was isolated, driedover MgSO₄ and evaporated under reduced pressure. Both INI-5 and INI-10were isolated by preparative column chromatography on a Prochrom LC80column, using Kromasil Si60A 10 μm and n.-hexane/ethyl acetate 70/30 aseluent. 5.4 g of INI-10 was isolated (R_(f): 0.51, eluent ethylacetate/hexane 30/70, Merck Kieselgel 60F₂₅₄). 3.87 g of INI-5 wasisolated (R_(f): 0.3, eluent ethyl acetate/hexane 30/70, Merck Kieselgel60F₂₅₄).

Photoinitiator INI-18

Acrylic acid4-(3-(2-[6-benzoyl-9-(2-ethyl-hexyl)-9H-carbazol-3-yl]-2-oxo-acetoxy)-2-hydroxy-propoxy)-butylester was synthesized according to the following synthesis scheme:

Hydrolysis of INI-2:

2.2 g (4.6 mmol) of INI-2 was dissolved in 20 ml ethanol. The reactionmixture was heated to 50° C. and 0.46 ml of a 10 N NaOH solution (4.6mmol) was added. The reaction was allowed to continue for three hours at50° C. The solvent was removed under reduced pressure and the residuewas dissolved in 10 ml water. The mixture was acidified with a 6Nhydrochloric acid solution. The mixture was extracted with 20 ml methyltert.butyl ether. The organic fraction was isolated, dried over MgSO₄and evaporated under reduced pressure. 2.1 g of the intermediatecarboxylic acid was isolated. The intermediate was used without furtherpurification.

Reaction with the Epoxy-Acrylate:

2 g (4.4 mmol) of the intermediate carboxylic acid was dissolved in 20ml acetonitrile. 10 mg BHT and 0.14 g (0.44 mmol) tetrabutylammoniumbromide were added and the mixture was heated to reflux. 0.9 g (4.4mmol) of 4-(glycidyloxy)butyl acrylate was added and the reaction wasallowed to continue for 16 hours at reflux temperature. The solvent wasremoved under reduced pressure and INI-16 was purified by preparativecolumn chromatography.

Photoinitiator INI-8

INI-8 was synthesized according to the following synthesis scheme:

Synthesis of the Oximes:

3.8 g (7.9 mmol) of INI-1 was dissolved in 34 ml pyridine and 22 mlethanol. 1.2 g (16.7 mmol) hydroxylamine chlorohydrate was added and thereaction mixture was refluxed for 16 hours. An additional 1.2 g (16.7mmol) hydroxylamine chlorohydrate was added and the reaction was allowedto continue for an additional three hours at reflux temperature. Thesolvent was evaporated under reduced pressure and the residue wasdissolved in 100 ml methylene chloride. The mixture was extracted with100 ml 1 N hydrochloric acid and twice with 100 ml water. The organicfraction was isolated, dried over MgSO₄ and evaporated under reducedpressure. The intermediate oxime was isolated by preparative columnchromatography on a Prochrom LC80 column, using Kromasil Si 60A 10 μmand a gradient elution from n.-hexane/ethyl acetate 70/30 ton.-hexane/ethyl acetate 50/50 at a flow rate of 150 ml/min. 1.4 g of theintermediate bis-oxime was isolated (R_(f): 0.5, eluent n.-hexane/ethylacetate 50/50, Merck Kieselgel 60 F₂₅₄).

Acylation of the Oximes:

1.2 g (2.36 mmol) of the intermediate oxime was dissolved in 20 mlmethylene chloride. 0.72 ml (5.19 mmol) triethyl amine was added,followed by the addition of 0.41 g (5.19 mmol) acetyl chloride. Thereaction was allowed to continue for 16 hours at room temperature. Thereaction mixture was extracted with 50 ml water, dried over MgSO₄ andevaporated under reduced pressure. INI-8 was purified by crystallisationfrom n.-hexane/ethyl acetate 60/40 (R_(f): 0.25, eluent: n.-hexane/ethylacetate 50/50, Merck Kieselgel 60 F₂₅₄).

Example 2

This example illustrates the high curing speed of radiation curablecompositions according to a preferred embodiment of the presentinvention.

Preparation of Radiation Curable Compositions

The comparative radiation curable compositions COMP-1 and COMP-2 and theinventive radiation curable compositions INV-1 to INV-4 were preparedaccording to Table 5. The weight % (wt %) was based on the total weightof the radiation curable compositions.

TABLE 5 wt % of INV-1 INV-2 INV-3 INV-4 COMP-1 COMP-2 DPGDA 43.0 38.042.0 37.0 46.5 41.5 TMPTA 40.0 40.0 40.0 40.0 40.0 40.0 EPD 7.5 7.5 7.57.5 7.5 7.5 IC127 — 5.0 — 5.0 — 5.0 INI-3 7.5 7.5 — — — — INI-4 — — 8.58.5 — — ITX — — — — 4.0 4.0 Dibutyl 2.0 2.0 2.0 2.0 2.0 2.0 phtalate

The free radical curable liquids COMP-1 and COMP-2 and INV-1 to INV-4were coated on a PET100 substrate using a bar coater and a 10 μm wiredbar. Each coated sample was cured using a Fusion DRSE-120 conveyer,equipped with a Fusion VPS/1600 lamp (D-bulb), which transported thesamples under the UV-lamp on a conveyer belt at a speed of 20 m/min. Thecuring speed was determined and is shown in Table 6.

TABLE 6 Radiation curable Curing speed composition (% of the maximumoutput) INV-1 50 INV-2 45 INV-3 50 INV-4 50 COMP-1 60 COMP-2 50

Example 3

This example illustrates that the radiation curable inkjet inksaccording to a preferred embodiment of the present invention can becured with a UV LED (395 nm) and do not have the undesirable yellowingbehaviour of ITX.

Preparation of Concentrated Pigment Dispersions DISP-1 and DISP-2

Concentrated Pigment Dispersions DISP-1: 45,000 g of DB162sol and 450 gof GENOSOL were dissolved in 31,050 g of DPGDA in a vessel of 125 Lusing a DISPERLUX™ disperser (from DISPERLUX S.A.R.L., Luxembourg).13,500 g of cyan pigment PB15:4 was added to the solution and stirredfor 30 minutes. The vessel was then connected to a Netzsch LMZ10 millhaving an internal volume of 10 L filled for 52% with 0.4 mm yttriumstabilized zirconia beads (“high wear resistant zirconia grinding media”from TOSOH Co.). The mixture was circulated over the mill for 7 hoursand 45 minutes at a flow rate of about 2 L per minute and a rotationspeed in the mill of about 15 m/s. During the complete milling procedurethe content in the mill was cooled to a temperature of 42° C. Aftermilling, the concentrated pigment dispersion DISP-1 was discharged intoanother 125 L vessel. The resulting concentrated pigment dispersionDISP-1 according to Table 7 exhibited an average particle size of 110nm.

TABLE 7 Component wt % PB15:4 15 DB162 15 GENORAD ™ 16 1 DPGDA 69

Concentrated Pigment Dispersions DISP-2: 15,000 g of S35000sol and 300 gof GENOSOL were dissolved in 8,850 g of DPGDA in a vessel of 60 L. 6,000g of cyan pigment PB15:4 was added to the solution and stirred for 30minutes using a DISPERLUX™ disperser (from DISPERLUX S.A.R.L.,Luxembourg). The vessel was then connected to a Bachofen DYNOMILL ECMPOLY mill having an internal volume of 8.2 L filled for 42% with 0.4 mmyttrium stabilized zirconia beads (“high wear resistant zirconiagrinding media” from TOSOH Co.). The mixture was circulated over themill for 1 hour and 50 minutes at a flow rate of about 5 L per minuteand a rotation speed in the mill of about 15 m/s. During the completemilling procedure the content of the mill was cooled to a temperature of54° C. The concentrated pigment dispersion DISP-2 was discharged intoanother 60 L vessel. The resulting concentrated pigment dispersionDISP-2 according to Table 8 exhibited an average particle size of 119nm.

TABLE 8 Component wt % PB15:4 20 S35000 20 GENORAD ™ 16 1 DPGDA 59

Preparation of Radiation Curable Inkjet Inks

The comparative radiation curable inkjet inks COMP-3 and COMP-4 and theinventive radiation curable inkjet inks INV-5 and INV-6 were preparedaccording to Table 9. The weight % (wt %) was based on the total weightof the radiation curable compositions.

TABLE 9 wt % of INV-5 INV-6 COMP-3 COMP-4 DPGDA — 64.6 — 69.0 VEEA 24.5— 30.0 — TMPTA 38.6 — 40.0 — GENORAD ™ 16 0.8 0.8 0.9 0.9 EPD 2.5 5.02.5 5.0 ITX — — 2.5 5.0 TPO — 5.0 — 5.0 IC907 4.0 — 4.0 — INI-1 9.5 9.5— — DISP-1 20.0 — 20.0 — DISP-2 — 15.0 — 15.0 BYK ™ UV3510 0.1 0.1 0.10.1

The comparative radiation curable inkjet inks COMP-3 and COMP-4 andinventive radiation curable inkjet inks INV-5 and INV-6 were coated onPGA-paper, using a bar coater and a 10 μm wired bar. The coated sampleswere mounted on a belt, transporting the samples under a Phoseon 4 W 395nm LED. The number of passes at a given belt speed to completely curethe samples was determined. The Q-tip method was used to determinecomplete cure. The results are summarized in Table 10.

TABLE 10 Radiation curable # passes at # passes at # passes atcomposition 5 m/min 20 m/min 30 m/min INV-5 1 2 2 INV-6 1 2 4 COMP-3 1 44 COMP-4 1 2 4

The inkjet inks with a more or less comparable sensitivity (INV-3, INV-4and COMP-4) were cured on a Fusion DRSE-120 conveyer equipped withFusion VPS/1600 lamp at 20 m/min at full power of the lamp. A secondsample was cured with a Phoseon 4 W 395 nm LED, passing the sample 4times under the LED at a speed of 5 m/min. The stability of the imagetone under both curing conditions was quantified by measuring the shiftin b-value between the freshly printed sample and the sample stored for7 days at ambient temperature. The results are summarized in Table 11.

TABLE 11 Radiation curable sample Δb (Fusion) Δb (LED) INV-5 1.5 2.7INV-6 2.0 3.2 COMP-4 3.4 5.7

From Table 11, it becomes apparent that the radiation curable inkjetinks according to preferred embodiments of the present invention have asignificantly more stable yellowing behaviour in comparison withthioxanthones for the same curing speed.

Example 4

This example illustrates the high curing speed of radiation curableinkjet inks according to a preferred embodiment of the presentinvention.

Preparation of Radiation Curable Inkjet Inks

The comparative radiation curable compositions COMP-5 and COMP-6 and theinventive radiation curable compositions INV-7 to INV-9 were preparedaccording to Table 12. The same concentrated pigment dispersions DISP-1and DISP-2 of EXAMPLE 3 were used. The weight % (wt %) was based on thetotal weight of the radiation curable compositions.

TABLE 12 wt % of INV-7 INV-8 INV-9 COMP-5 COMP-6 DPGDA — 70.5 64.6 — 69VEEA 24.5 — — 30.0 — TMPTA 38.6 — — 40.0 — GENORAD ™ 16 0.8 0.9 0.8 0.90.9 EPD 2.5 2.5 5.0 2.5 5.0 ITX — — — 2.5 5.0 TPO — — 5.0 — 5.0 IC9074.0 4.0 — 4.0 — IC379 3 INI-2 9.5 4.0 9.5 — — DISP-1 20.0 — — 20.0 —DISP-2 — 15.0 15.0 — 15.0 BYK ™ UV3510 0.1 0.1 0.1 0.1 0.1

The inkjet inks INV-7 to INV-9 and COMP-4 and COMP-6 were cured on aFusion DRSE-120 conveyer equipped with Fusion VPS/1600 lamp (D-bulb) at40 m/min at full power of the lamp. The degree of curing was evaluatedusing a Q-tip. A sample was considered as fully cured at the momentscratching with a Q-tip caused no visual damage. The results aresummarized in Table 13.

TABLE 13 Radiation curable Degree of curing at 40 sample m/min INV-7Fully cured INV-8 Fully cured INV-9 Fully cured COMP-5 Fully curedCOMP-6 Fully cured

From Table 13, it becomes apparent that the radiation curable inkjetinks according to preferred embodiments of the present invention arehighly sensitive.

Example 5

This example illustrates that the radiation curable inkjet inksaccording to preferred embodiments of the present invention exhibit ahigh curing speed and do not have the undesirable yellowing behaviour ofITX.

Preparation of Radiation Curable Inkjet Inks

The comparative radiation curable compositions COMP-7 and COMP-8 and theinventive radiation curable compositions INV-10 to INV-14 were preparedaccording to Table 14. The same concentrated pigment dispersions DISP-1and DISP-2 of EXAMPLE 3 were used. The weight % (wt %) was based on thetotal weight of the radiation curable compositions.

TABLE 14 wt % of INV-10 INV-11 INV-12 INV-13 INV-14 COMP-7 COMP-8 DPGDA— 64.6 — 66.5 — — 69.0 VEEA 24.5 — 26.5 — 24.5 30.0 — TMPTA 38.6 — 38.6— 38.6 40.0 — GENORAD ™ 0.8 0.8 0.8 0.9 0.8 0.9 0.9 16 EPD 2.5 5.0 2.55.0 2.5 2.5 5.0 ITX — — — — — 2.5 5.0 TPO — 5.0 — 5.0 — — 5.0 IC907 4.0— 4.0 — 4.0 4.0 — INI-5 9.5 9.5 — — — — INI-10 — — 7.5 7.5 — — — INI-8 —— — — 9.5 — — DISP-1 20.0 — 20.0 — 20.0 20.0 — DISP-2 — 15.0 — 15.0 — —15.0 BYK ™ 0.1 0.1 0.1 0.1 0.1 0.1 0.1 UV3510

The comparative radiation curable compositions COMP-7 and COMP-8 andinventive radiation curable compositions INV-10 to INV-14 were coated onPGA-paper, using a bar coater and a 10 μm wired bar. The coated sampleswere mounted on a belt, transporting the samples under a Phoseon 4 W 395nm LED at a speed of 5 m/min and 10 m/min respectively. The degree ofconversion was determined. The results are summarized in Table 15.

TABLE 15 Radiation curable Degree of conversion Degree of conversionsample at 5 m/min at 10 m/min INV-10 84 78 INV-11 94 88 INV-12 79 72INV-13 87 80 INV-14 83 76 COMP-7 85 76 COMP-8 94 89

From Table 15, it becomes clear that the initiators according to apreferred embodiment of the present invention result in a comparabledegree of conversion compared to thioxanthone based compositions with acomparable composition (INV-10, INV-12, INV-14 and COMP-7; INV-11,INV-13 and COMP-8).

High contents of thioxanthone in radiation curable compositions areknown to give high sensitivity for LED curing but result in an instableyellowing behaviour. Therefore, the comparative radiation curablecomposition COMP-8, having a high ITX content, and the correspondinginventive radiation curable compositions INV-11 and INV-13 were studiedmore in depth for their yellowing behaviour.

The radiation curable compositions INV-11 and INV-13 and COMP-8 werecured with a Phoseon 4 W 395 nm LED, passing the sample 4 times underthe LED at a speed of 5 m/min. The stability of the image tone wasquantified by measuring the shift in b-value between the freshly printedsample and the sample stored for 7 days at ambient temperature. Theresults are summarized in Table 16.

TABLE 16 Radiation curable sample Δb INV-11 −3.64 INV-13 −3.17 COMP-8−8.02

From Table 16, it becomes apparent that the photoinitiators according topreferred embodiments of the present invention have a significant morestable yellowing behaviour compared to thioxanthones.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1-15. (canceled)
 16. A free radical radiation curable composition for UVLED curing comprising: at least one co-initiator selected from the groupconsisting of an aliphatic tertiary amine and a dialkyl anilinederivative; and at least one photoinitiator according to Formula (I):

wherein, R1 and R2 are independently selected from the group consistingof an aromatic or heteroaromatic group and a substituent according toFormula (II):

R3 is selected from the group consisting of hydrogen, an alkyl group, analkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, andan aryl or heteroaryl group; S₁ and S₂ are independently selected fromthe group consisting of hydrogen, an alkyl group, an alkenyl group, analkynyl group, an aralkyl group, an alkaryl group, an aryl group, aheteroaryl group, a halogen, OH, an alkoxy group, a thiol group, athioalkoxy group, an ester group, an amide group, an amine group, and acarboxylic acid group; Y represents O or NR5; R4 and R5 are selectedfrom the group consisting of hydrogen, an alkyl group, an alkenyl group,an alkynyl group, an aralkyl group, an alkaryl group, and an aryl orheteroaryl group; n and m independently represent an integer from 1 to3; and X and Z represent O.
 17. The radiation curable compositionaccording to claim 16, wherein at least one of R1 and R2 is representedby a substituent according to Formula (II).
 18. The radiation curablecomposition according to claim 16, wherein S₁ and S₂ represent hydrogen.19. The radiation curable composition according to claim 17, wherein S₁and S₂ represent hydrogen.
 20. The radiation curable compositionaccording to claim 16, wherein R3 represents an alkyl group.
 21. Theradiation curable composition according to claim 17, wherein R3represents an alkyl group.
 22. The radiation curable compositionaccording to claim 18, wherein R3 represents an alkyl group.
 23. Theradiation curable composition according to claim 20, wherein R3represents a branched alkyl group.
 24. The radiation curable compositionaccording to claim 16, wherein the at least one photoinitiator is adiffusion hindered photoinitiator selected from the group consisting ofa polymerizable photoinitiator, a multifunctional photoinitiator, apolymeric photoinitiator, and an oligomeric photoinitiator.
 25. Theradiation curable composition according to claim 24, wherein the atleast one photoinitiator according to Formula (I) comprises at least onepolymerizable ethylenically unsaturated group.
 26. The radiation curablecomposition according to claim 25, wherein the at least onepolymerizable ethylenically unsaturated group is selected from the groupconsisting of an acrylate, a methacrylate, an acrylamide amethacrylamide, a styrene, a maleimide, a vinyl ester, a vinyl ether, anallyl ether, and an allyl ester.
 27. The radiation curable compositionaccording to claim 26, wherein the at least one polymerizableethylenically unsaturated group is an acrylate.
 28. The radiationcurable composition according to claim 24, wherein at least one of R1 toR3 is substituted with the at least one polymerizable ethylenicallyunsaturated group.
 29. The radiation curable composition according toclaim 24, wherein one of the groups selected from R1 to R3, S₁, and S₂is linked to a polymer selected from the group consisting of a starpolymer, a dendritic polymer, and a hyperbranched polymer.
 30. Theradiation curable composition according to claim 29, wherein thehyperbranched polymer is a polyether or a polyester.
 31. A radiationcurable inkjet ink comprising: the radiation curable compositionaccording to claim
 16. 32. A radiation curable inkjet ink comprising:the radiation curable composition according to claim
 24. 33. A methodfor preparing a radiation curable composition as defined by claim 16comprising the steps of: a) providing a composition containing monomers;and b) adding to the composition the at least one photoinitiatoraccording to Formula (I) and the at least one co-initiator selected fromthe group consisting of an aliphatic tertiary amine and a dialkylaniline derivative.
 34. A method for preparing a radiation curablecomposition as defined by claim 24 comprising the steps of: a) providinga composition containing monomers; and b) adding to the composition theat least one photoinitiator according to Formula (I) and the at leastone co-initiator selected from the group consisting of an aliphatictertiary amine and a dialkyl aniline derivative.